X-ray diffraction experiments are particularly well suited to the structural characterization of homogeneous, inhomogeneous and heterogeneous materials, since the used wavelength of the X-ray beam is of the same order of magnitude as the characteristic spacings in the material to be examined. Experts know that the penetrating X-rays interact elastically with the material and that constructive interference effects can only be observed when the Bragg equation (nλ=2d*sin(2θ/2)) is satisfied under specular conditions (n denotes the integer ordinal number, λ the wavelength, θ the scattering angle, and d denotes the characteristic spacings for the material, for example the lattice planes, or molecular spacings). The experimental results show the characteristic diffraction pattern, which depends on the structure of the material being investigated. The diffraction pattern is used to make predictions as regards the qualitative and quantitative crystal properties of the sample being investigated.
X-ray diffraction (XRD) is a special way of carrying out these material investigations and can be conducted in transmission or reflection geometry. The X-ray beam impinges upon the sample at specific scattering angles θ which are continuously changed in the experiment (reflection geometry), or the beam is passed through the sample (transmission geometry).
X-ray experiments for elucidating the structure of materials can be carried out either using large facilities such as a synchrotron or linear accelerator, or using so-called laboratory instruments such as standard X-ray diffractometers or small table-top X-ray diffractometers (benchtop X-ray diffractometer). Typical laboratory instruments consist of a radiation source, primary side and secondary side X-ray optics, a sample alignment or adjustment device and a detector unit. Because X-ray tubes are used as the source of radiation, such X-ray laboratory instruments have to be designed as full-protection machines. This means that, for example in Germany, the legally set maximum permissible local dose rate of 3 microsieverts per hour (μSv/h) at a distance of 0.1 meters from the completely closed protective housing must not be exceeded (http://www.bfs.de/de/bfs/dienstleitungen/baz/Baz_roev). To operate the X-ray source, existing laboratory X-ray machines require a cooling circuit which usually employs a sealed external fluid circuit, in addition to a specially secured power supply. In order to satisfy the legal requirements for X-ray full-protection devices, it is necessary for these connections to be fed from outside to the X-ray source, depending on the construction of the full-protection machine, via special, secure routes into the machine chamber. In contrast, so-called benchtop X-ray diffractometers are small, compact table-top machines which are usually powered from the standard mains supply, usually do not require an external cooling circuit and thus do not include any external cooling fluid connections. For this reason, benchtop X-ray diffractometers are marketed as simple, transportable full-protection machines which are easy to install, are flexible as regards quality control or can be used as a laboratory instrument for scientific/educational purposes.
Diffraction patterns resulting from the X-ray diffraction experiment vary widely with sample temperature. In the field of material characterization using X-ray diffraction (XRD), investigating the structural properties of materials as a function of temperature has proved to be particularly auspicious, since improved characterization of the material under investigation can be obtained, for example under manufacturing and application conditions. For this reason, a large number of sample temperature control chambers already exist for standard laboratory diffractometers or for synchrotron applications, which are positioned between the X-ray source and the detector. In this respect, the manner of heating and/or cooling the sample in the heating chamber is crucial.
A variety of heatable sample chambers for standard laboratory diffractometers or synchrotron applications are known in the prior art (see, for example, DE 20109573 U1, JPH 0342561 A, DE 102004029721 A1, WO 2013/005180 A1, WO 00/23795 A1, and DE 202004007301 U1). However, these suffer from several disadvantages which render the use of heating chambers of this type in fully protected benchtop X-ray diffractometers impossible. The external cooling circuits of known X-ray heating chambers and their open loop control and closed loop control units and gas flow hook-ups cannot be used in benchtop X-ray diffractometers. The major advantage of the benchtop X-ray diffractometer is that such a sealed, fully protected machine can be used without external cooling circuit connections, without special power supplies and can be readily transported, since they do not require any additional operational and power connections at the location of measurement. The temperature control chambers described in the prior art cannot be used in small benchtop machines, not only because of their geometric dimensions and their weight, but also because they do not comply with the safety requirements for a full-protection machine, since in order to operate the temperature control chambers described in prior art, a variety of external connections are required which are not available in a fully protected machine of table-top dimensions. Particularly problematic in this instance is the feed-through for the coolant.
There may be a need to overcome the disadvantages of the prior art mentioned above and to provide a sample temperature control chamber which can be used with compact benchtop X-ray machines and full-protection X-ray machines in a simple manner and while complying with the safety requirements.